1. Field of the Invention
The present invention relates to a rod lens array in which a plurality of rod lens elements are arranged between two side panels and a resin is filled and cured in spaces between the rod lens elements to be integrally formed and a method of manufacturing the same. Particularly, the present invention relates to a rod lens array which improves an arrangement, optical performance, and the weatherability of lens elements, by using a glass fiber reinforced epoxy resin which is used as the side panels and a phenol-based curing agent which is used as a curing agent of the epoxy resin as well as by using an additional reaction type silicone resin which contains a spherical organic filler monodispersed and whose viscosity is adjusted, as the resin for filling the spaces.
2. Related Art
As well known in the art, a rod lens array has a structure in that a plurality of minute gradient index rod lens elements are arranged between two side panels and a resin is filled between spaces of the lens elements to be integrally formed to each other, and is an example of optical components for forming a single continuous erected unit magnification image. Since such a rod lens array has a short optical path length and needs no inverting mirror, it is possible to make the device be smaller. Because of the size-reducing feature, the rod lens array is commonly used as an optical component not only for an image reading system such as a facsimile, an image scanner, a copier, etc which forms images, but also for an image writing system that forms a latent image on a photoreceptor in accordance with supplied image signals. Recently, high resolution has been accelerated, and the requirements for higher precision in latent image and for better quality in terms of the precision of the position in which an image is formed increase.
Conventionally, this type of rod lens array is manufactured by a method as disclosed in JP 61-55610A. For example, a spacer which is used as a reference for arrangement is provided on a substrate, and a predetermined number of fiber lens elements are arranged so as to form one or more lines along a surface of the substrate by using the spacer as a reference. After arranging the lens elements in an array, a temporary spacer is disposed so as not to disturb the arrangement, and another substrate is used as a cover to press the lens elements. In this state, a resin is filled into the spaces of the lens elements to keep the shape and satisfy the optical performance. Thereafter, a lens block which is integrally formed by the cured resin is cut to a predetermined lens length, and both cut edges are ground.
Here, a glass fiber reinforced plastic (FRP) is used as the side panel, and particularly, a glass fiber reinforced epoxy resin panel is extensively used (refer to. JP-A-2001-318208) on the following grounds.
(a) It is necessary that a thermal expansion coefficient of the side panel is similar to that of a material of the lens so that undesirable arrangement of the lens elements is prevented during heat treatment after filling of the resin.
(b) It is necessary that grindability of the side panel is similar to that of the material of the lens because the side panel must be ground like the lens elements.
(c) Use of a panel glass may be considered because the material of the lens is glass, but the panel glass is difficult to handle because the panel glass is easily broken.
In this case, since the rod lens arrays are cut from a lens block by one after filling and curing of the resin, the side panel must be made of a material having excellent heat resistance. Accordingly, in related art, a curing agent used to produce a glass fiber reinforced epoxy resin panel is limited to acid anhydrides or heat-resistant amines so that the glass fiber reinforced epoxy resin panel is sustained in a process at bout 200° C. Furthermore, if the above-mentioned curing agents are used, the calcination treatment is conducted after curing of the resin so as to stabilize a quality of the glass fiber reinforced epoxy resin panel. For example, the calcination treatment is conducted at about 200° C. for several tens hours while a load is applied thereto.
However, the rod lens array in which the glass fiber reinforced epoxy resin panel is used as the side panel has a problem in that a waterdrop-shaped extraneous substance is formed on a surface of the lens elements after a weatherability test (dampproof test) and acts as a lens, thus significantly reducing optical properties.
Further, there is a problem in that a glass cloth of the glass fiber reinforced epoxy resin panel comes off the panel and thus increases unevenness of a surface thereof, causing the precision of arrangement of the lens elements to be deteriorated.
Additionally, there are problems in that a surface of the glass fiber reinforced epoxy resin panel is stained by an adhesive (cyanoacrylates) used during a production process when an amine-based curing agent is used as an oxidizing agent and that high temperature heating and cleaning are necessary for a long time in order to remove the adhesive, resulting in poor productivity.
Turning to the filler provided between the side panels, the resin which is filled in order to support the fiber lens elements to each other includes an epoxy resin or a silicone resin. As for the resin, a desired amount of inorganic filler is added thereto in order to improve the cutting performance while cutting. Further, the viscosity of the resin is comparatively high, for example, 2500 to 3000 mPa·s and the resin is filled by suction.
In recent years, in order to form an image with a high resolution and less irregularity, it is required to decrease the lens diameter (for example, 0.6 mm or less). However, if the resin used in the related art is used, there are problems in that in the case of a lens with a small diameter, the positions or directions of the lenses may be irregular (that is, arrangement performance is lowered). The above problems may arise due to the space becoming small according to the small lens diameter, difficulty in filling the resin into the space, limited time available, thickening during filling, and increased viscosity resistance. When using the epoxy resin, the lens arrangement is disturbed due to the shrinkage amount of the curing being increased, and thus the optical performance is lowered and the position where the image is formed is deviated.
There are further problems in that a resin is not completely filled in all of the portions to cause optical deterioration. These problems may be caused by the weak flowability of resin due to high thixotropy and high viscosity of the epoxy resin, aggregation of the inorganic filler or clogging of the resin.
Further, due to the high viscosity of resin, the spaces of the lens elements having small diameter become smaller, it takes a long time to fill the spaces, and the workability is lowered. Since the adhesive component of the resin is not suitable for the lens element (glass) and the substrate (FRP: glass fiber reinforced plastic), there are problems in that the adhesive force of the lens array is not strong such that the adhering failure frequently occurs.